The present invention relates to dihydro gamma ionone and homologues thereof and mixtures of dihydro alpha ionone, dihydro beta ionone and dihydro gamma ionone and alkyl homologues thereof produced by a novel process, as well as the intermediates used in said novel process. Dihydro alpha ionone, dihydro beta ionone and dihydro gamma ionone and homologues thereof are useful in augmenting and/or enhancing the flavor and/or aroma of consumable materials such as foodstuffs, tobaccos, perfumes, colognes and perfumed articles.
Prior to our invention, dihydro gamma ionone was produced by means of a method such as that described in British Pat. No. 794,416 published on May 7, 1958. That is, alpha ionone is reduced in the presence of Raney nickel to form dihydro-alpha-ionone. The dihydro-alpha-ionone is then reduced with lithium aluminum hydride to form dihydro-alpha-ionol. The dihydro-alpha-ionol is then acetylated to form dihydro-alpha-ionol acetate. Hydrogen chloride is added to the resulting dihydro-alpha-ionol acetate thus yielding 3-chloro-tetrahydroionyl acetate. The 3-chloro-tetrahydroionyl acetate is then treated with potassium laurate thereby producing a mixture of dihydro gamma-ionyl acetate, dihydro alpha-ionyl acetate and dihydro-beta-ionyl acetate. The resulting mixture of dihydro ionyl acetates is then saponified to the corresponding alcohols. This mixture of alcohols is then oxidized with such oxidizing agents as chromic acid to yield a mixture of dihydro ionones, dihydro alpha ionone, dihydro beta ionone and dihydro gamma ionone.
Dihydro gamma ionone is a constituent of ambergris. It has a warm, woody, earthy aroma; the alpha isomer on the other hand has a sweet, floral, woody note. The mixture of dihydro ionones produced according to British Pat. No. 794,416 has a woody, ionone like, floral, sweet, fruity and bitter flavor profile. In addition to dihydro gamma ionone being used in fragrances as part of an ambergris replacement, dihydro gramma ionone is also useful for cyclization to "ambrinol" in high yield.
Accordingly, a need has arisen in the perfumery and flavor industries for an efficient and inexpensive method for producing dihydro gamma ionone and homologues thereof as well as mixtures containing dihydro gamma ionone or homologues thereof, dihydro beta ionone or homologues thereof and dihydro alpha ionone or homologues thereof, respectively. Our invention has fulfilled that need.
The protection of a carbonyl functional group during hydration or cyclization using nitrogen containing protecting groups for the carbonyl function is well known in the prior art. Thus, Ogawa, et al. in Japanese Pat. No. 7,208,049 and French Pat. No. 2,146,563 discloses a process for preparing hydroxy citronellal by treating citronellal with a primary or secondary aliphatic amine or amino alcohol, hydrating the adduct with aqueous acid and hydrolyzing the resulting imine or immonium group using a base. One of the products formed in situ is the oxazolidine intermediate. This is disclosed in detail on page 109, J. Org. Chem., Volume 39, No. 1, 1974 at Scheme 2.
Cyclization of gamma dihydro ionone to ambrinol according to the reaction using boron trifluoride etherate is known in the prior art: M. Stoll and M. Hinder, Helv. Chem. Acta., 38, 1593 (1955).
A reaction is described by Stoll, Helv. Chim. Acta 38, 1587-92 (1955). U.S. Pat. No. 2,933,506 issued on Apr. 19, 1960 describes the reaction: ##STR3## At Column 3, Lines 39-47 it is stated that when using a myrcene adduct according to Formula III, which is an aldehyde characterized by having a hydrogen atom at R.sub.1 (while R.sub.2, R.sub.3 and R.sub.4 may also be hydrogen or may be substituted by other organic groups), the carbonyl group is preferably protected from the action of the acid cyclization reagent. For this purpose it is stated that the aldehyde group is advantageously and temporarily converted into the azomethine group by condensing the aldehyde with an amine such as an aromatic amine such as aniline. It is further stated at lines 49-57 that following cyclization of the myrcene adduct of Formula III with the protected aldehyde group, the entire reaction mixture is blown with steam for a few minutes whereby the Shiff base is split up into the cyclic aldehyde of Formula IV and the amine used for protection.
However, notwithstanding the disclosures of the prior art nothing in the prior art even implicitly indicates the production of dihydro gamma ionone and homologues thereof according to the low cost efficient process of our invention.